Brush type high velocity air-fuel burner



May 17, 1966 M. L. THORPE ETAL 3,251,394

BRUSH TYPE HIGH VELOCITY AIR-FUEL BURNER Filed Dec. 10, 1963 2Sheets-Sheet 1 III OOOOOOOOOOOQOOOOOOOOOOOOOOOOO May 17, 1966 M. L.THORPE ETAL 3,251,394

BRUSH TYPE HIGH VELOCITY AIR-FUEL BURNER 2 Sheets-Sheet 2 Filed Dec. 10,1965 burner, particularly of the brush or ribbon type.

United States Patent 3,251,394 BRUSH TYPE HIGH VELOCITY AIR-FUEL BURNERMerle L. Thorpe, R.F.D. 1, and Kent W. Harrington, Dear-born Road, bothof Suncook, NH. Filed Dec. 10, 1963, Sell. No. 329,483 9 Claims. (Cl.15827.4)

This invention relates to brush or ribbon type burners and moreparticularly to air-fuel burners which, due to high velocity, have veryhigh heat transfer rates, heretofore available only from expensiveoxygen flames or electric arcs.

Burners of this invention are to be distinguished from post orditfusionburners, whose flames have restricted velocity ranges, oftennot exceeding 150 feet per second with air or 600 feet per second withoxygen, due to the necessity of maintaining the velocity low enough tostabilize the post-burning flame.

Burners in accordance with this invention operate with rocket-type jets,being deliberately operated under conditions of flash back to a pressurechamber. As a result, the upper range of exit velocity is in no waylimited by flame extinguishment considerations, since maintenance of apost-burning flame is not essential to continued operation, and littlediffusion burning occurs.

When exit velocities can thus be raised, greater opportunity is affordedfor utilizing air (21% 0 as distinguished from more concentrated oxygen,as the combustion sustaining material, without decreasing heat transferperformance. Air-fuel combustion products, at flame temperature, ifgiven high enough velocity (upwards of 2000 feet per second) have heattransfer characteristics which substantially equal the heat transferproduced in a conventional post-burning oxygen flame. The cost perB.-t.u. transferred to the work is, however, so much less for air thatsubstantial savings result with no loss in speed or efiiciency, so faras the work is concerned, as when the burner is used for stippling,thermally texturing, or spalling rock surfaces. Additionally, the highvelocity jets have a scrubbing effect which is highly beneficial in3,251,394 Patented May 17, 1966 FIG. 6 is a fragmentary cross-sectionalview taken along the line 66 of FIG. 2;

FIG. 7- is a perspective view of part of one of the elements shown inthe previous figures; and

. FIG. 8 is a diagrammatic view of a water jet accessory for use withthe burner. v The burner comprises a cylindrical tube 14 of a hightemperature alloy (such as standard 310 stainless steel pipe). Aroundthe ends of the pipe are bolted rings 16 and 17 which provide seats forend caps 18 and 20, respectively, which are bolted to the rings with theintervention 7 of gaskets (not shown).

such operations as rock stippling or descaling steel plate. 7

The attainment and maintenance of these high velocities, whileimpossible in fuel-air post burning apparatus because of flameextinguishment at such velocities, are not readily achieved either in aminiature rocket-type These high velocities cause flame blowouts withinthe chamber, uneven gas distribution along the exit orifices, andexcessive oscillation and resonance.

It is a primary object of this invention to provide a miniature air-fuelrocket-type brush or ribbon type burner which has stability withoutresonance at high through: puts producing a ribbon-like row of gaseousjets having heat transfer rates comparable to those of oxygen flames.

I have discovered that by utilizing a combination of features ashereinafter described, reliable and satisfactory operation of suchminiature air-fuel type rocket burners can be achieved with high jetvelocities and good stability.

A burner embodying the combination of this invention is illustrated inthe accompanying drawings, wherein:

FIG. Us a side elevational view, partly in cross-section, of a burner inaccordance with the invention, broken away to indicate extent;

FIG. 2 is an end elevational view of the lower part of the burner shownin FIG. 1';

FIG. 3 is a bottom view of the burner shown in FIG. 1;

FIG. 4 is a cross-sectional view of portions of the burner;

FIG. 5 is a cross-sectional view taken along the line 5-5 of FIG. 4;

Each of the caps 18 and 20 has a tap ed bore, 26, 27, respectively,communicating with ports 32 and 34 leading to off-center inlets leadinginto the interior of the chamber formed by the capped tube 14.

Each end cap is also drilled and countersunk to accommodate a bolt 36and 38, respectively, which supports a flame stabilizer 40, one at eachend of the chamber.

Lefthand stabilizer 40 has a hub portion 41 which is offset so that itsouter end can be inserted into an axial bore in the end cap with itsoifset seated against the internal wall 42 of the end cap. The hubterminates at its inner end in a thin disc which fits into the internalbore of cylinder 14. The disc is drilled to provide a series ofapertures 46 equally spaced about the disc with the bores being at anangle to the axis of the tube, for example, 45, inwardly of the disc.Preferably each disc has 7 apertures 46 on 45 centers omitting anyaperture at the bottom of the disc as shown in FIG. 5; Additionally, thestabilizer 40 has a pair of smaller axial apertures 48 spaced radiallyoutwardly from and between each adjacent pair of inclined apertures 46.A row of 30 aligned apertures forming exhaust nozzles 50 are providedbetween the inner ends of the stabilizers 40.

Screw threaded couplings 52 extend from the threaded bores 26' and 27for attachment of metal tubes 60 and 62 which lead upwardly into theinterior of a handle 64 for communication with a common source 66 of afuel-air mixture.

Soldered to the outside of the cylindrical tube 14, as .by a hightemperature silver solder 'having a melting point of at least 1100 F.,is a long length of copper tubing 70 having the configuration shown inFIG. 7. An inlet end 71 of the tube proceeds downwardly around one sideof the burner and then longitudinally of the burner close and inparallel relation to the row of aper-- tures 50 to the other end of theburner; then upwardly on the same side of the burner and longitudinallyback across the top of the burner; then around the other side of the endof the burner; back again longitudinally of the burner in parallelrelation to the apertures 50 on the other side; then upwardly around theother side of the burner and to an outlet end 72. As shown in FIG. 1,the inlet 71 and outlet 72 may continue up through the interior of thehandle 64 for connection to a source'of water or other cooling fluid andman exhaust so that the cooling fluid may be circulated through thetubing during operation of the burner.

The symmetrical arrangement of the cooling tube about the axis of thehousing is an important feature of the invention. If cooling tubing islocated only adjacent the exhaust orifices, the stresses set up in therest of the housing when heated to the temperatures contemplated forproper operation in accordance with this invention, namely, upwardsof1000 F., soon cause a warping or bending of the tube which severelylimits its life. By cooling the housing along its length diametricallyopposite to the row of orifices as well as in the area of the orifices,such buckling of the housing is overcome. Normally, with the wallsoperating at a temperature of 1400l500 F., the cooling medium can holdthe bottom and top sections of the tube at 500 F. or less, withoutcausing more than percent heat loss and usually only about 3.5 percentheat loss to the cooling fluid, which is perfectly feasible in a burnerwhich generates, as does the embodiment shown in the drawing, upwards of10,000 B.t.u.s per minute.

Also, to aid ignition, the bolt 38 has an axial bore 80 whichcommunicates with an axial bore 81 through the righthand stabilizer 40and with an annular recess 82 surrounding the bolt 38 near its head, therecess registering with an outwardly extending passageway 83 leading toa tapped bore 84 in cap for reception of a tube 85 which also leadsupwardly through the handle 64 for connection to a source of oxygen.

In the particular construction shown the nozzles 50 comprise 30 inchholes on inch centers. The stabilizer apertures 46 are inch in diameter,and apertures 48 are each inch in diameter. All other parts are shown toapproximate scale with respect to a tube of approximately 2.375 inchesOD. and 2.067 ID. The ratio of about 3.14 sq. in. internalcross-sectional area of the tube to the 0.264 cross-sectional area ofthe inlets at one end of the tube is thus about 12:1; or about 6:1 withrespect to the total cross-sectional area of the inlets at both ends ofthe tube. The ratio of exit to total injection cross-sectional area isapproximately 1.29:0.528 or 2.45. If this ratio is decreased, operationbecomes less and less satisfactory. As the ratio is increased, thechamber pressure decreases at a constant through-put with resultingreduction in exit velocity and reduced heat transfer so that the ratioshould be maintained at not more than 8:1. Given a proper exit toinjection cross-sectional area ratio, such as the above, chamberpressure may run up to 50 pounds per square inch or higher, dependingupon the intended use and permissible jet velocity.

The cooling system is operated to maintain the burner walls at between1000 and 2200 F., preferably 1400 to 2000 F. It has been found that at2000 F. throughput can be raised to 250 cubic feet per minute ascontrasted with only 20-40 c.f.m. with a 200 F. wall, but operation at1400 F. is readily achievable with 125 c.f.m. through-put and jetvelocities of 5001500 feet per second.

The cross-sectional area of the housing controls the through-put foroptimum operation. This is because complete combustion is essential tosuccessful operation, and too great input will result in incompletecombustion with the walls then operating too cool. The approximate 2inch diameter housing shown has a cross-sectional area of about 3.14square inches. This cross-sectional area is more than is needed for acubic feet per end per minute input, being a .0628 ratio and is betteradapted for a 50 cubic feet per end per minute input with a ratio of.0314 and is probably not enough for an input of 100 cubic feet per endper minute or a ratio of .0157. The lower limit of the ratio of tubecross-sectional area to cubic feet of air per minute should thereforenot be less than about .02. Or, to put it in another way, thecrosssectional area of the tube should preferably not be less than 1square inch for each 25 cubic feet input of combustible fuel-air mixtureper end per minute.

While the diameter of the combustion chamber may vary, anything lessthan /4, inch LD. would not be considered satisfactory.

This burner has been found extremely eflicacious and efiicient instippling rock, specifically granite. For this purpose, the burner ismounted on an indexing carriage which traverses back and forth inprogressively parallel paths over a prepared granite surface, forexample, lengthwise of an oversize 4-foot-by-8-foot slab. The jetsimpinge perpendicularly downwardly onto the surface regardless of thedirection of relative travel, thus aiding in securing uniform stipplingon all traverses. The orifices should be kept as close as possible tothe granite surface, not more than A2 inch, which means that the coolingtubing has to be less than /2 inch in diameter. Preferably,

they are outside diameter so there is about inch clearance duringoperation. With a chamber pressure of about 3 pounds p.s.i., the jets,if unopposed, are about 2 inches long when the burner is operated from a40- pound source of combustible air and natural gas mixture producing ajet velocity of above 600 feet per second. The closer the stand-01f, theless the heat loss. Operating under these conditions, the burner maytraverse a hardto-spall block granite surface at about 7 feet a minutecan be increased up to 8.8 feet per minute at the 5-p0und pressure.

Also, because of the abrading effect encountered during stippling, thecopper tubing on each side of the orifices should be on about inchcenters to prevent the space between the tubes from becoming cloggedwith melted slag. Making the bottoms of the tubing wall as thick aspossible is helpful in prolonging life due to abrasion; or thin stripsof metal may be added to the bottoms of the cooling tubes to offer greatthickness to prolong life against sand blast abrasion losses.

Since some granite slabs are only 1 or 2 inches thick and can crack whensubjected dry to the heat transfers contemplated in the operation of theburner, it is desirable to wet the surface of the granite as by a waterspray directed downwardly onto the surface of the granite at an angle infront of and behind the jets. This preand post-wetting of the surface inno way affects the stability of the burner operation, since the jetblast quickly clears the area beneath the jets. This is in contrast topost burner stippling devices, where the flame velocities are so lowthat they are badly affected by water sprays which can cause flameextinguishment. Moreover, a water spray traveling in front of the burnerwashes away all chips to insure that the jets impinge on cleaned stone.Thus, in FIG. 8 there is shown a water pipe surrounding the burner onsupports 92 and having orifices which direct water jets as shown at anangle down onto the slab 91 being treated in advance of and rearwardlyof the burner.

While the embodiment shown in the drawing has a straight single row ofuniformly spaced exhaust orifices having parallel axes, it iscontemplated that their spacing, axis orientation, and individual sizemay be varied, and that more than one row may be utilized, all dependingupon the type of operation and end results desired.

As can be seen, one of the great advantages of burners which operatewith an air-fuel mixture is that the jets, where a flame temperature of3000 F. is developed, contain 78 percent nitrogen and therefore havemuch more mass than is present in a jet which constitutes the reactionproducts of oxygen-fuel-rnixtures at the same 3000" F. temperature. Theadditional mass is of course useful in displacing surface material, forexample, in stippling spallable rock surfaces.

What is claimed is:

1. An internal combustion burner comprising a hollow cylinder of maximumwall thickness less than the maximum internal cross-dimension of saidcylinder, cap means plugging both ends of said cylinder, :1 row ofspaced exhaust orifices extending along one side of said cylinder, aplurality of inlets leading into said cylinder for injecting anair-fluid fuel combustible material continuously into said cylinder forcombustion within said cylinder with discharge of the products ofcombustion through said exhaust orifices, and the total cross-sectionalexit area of said exhaust orifices exceeding the total cross-sectionalinlet area of said inlets, and a pair of flame stabilizers, one at eachend of said tube, said stabilizers comprising apertured discs extendingtransversely of said tube in spaced relation to the inside walls of saidcap means.

2. A burner as claimed in claim 1, wherein the stabilizers includeapertures whose axes are inclined relative to the axis of said cylinder.

3. A burner as claimed in claim 1, wherein the stabilizers are locatedbeyond the ends of the row of exhaust orifices.

4. The method of stippling a spallable rock surface comprising wettingsaid surface with water, traversing said Wet surface transversely with arow of impinging, closely spaced, concentrated high temperature gaseousjets directed perpendicularly downwardly onto said wet surface, saidjets comprising the substantially complete prodnets of combustionreaction of an air-fluid fuel mixture, discharged continuously from acommon internal combustion chamber at substantially uniform velocitiesexceeding 500 feet per second, wherein said surface is Wetted with waterby directing a series of jets onto said surface at an angle thereto justprior to traversing said surface with said gaseous jets.

5. An internal combustion burner comprising a hollow tube of maximumwall thickness less than the maximum internal cross-dimension of saidtube, cap means plugging both ends of said tube, exhaust orifice meansextending along one side of said tube, an inlet leading into said tubeat each end thereof for injecting an air-fluid fuel combustible mixturecontinuously into said tube from opposite ends thereof for combustionwithin said tube with discharge of the products of combustion throughsaid exhaust orifices, and the total cross-sectional exit area of saidexhaust orifices exceeding the total cross- 1 sectional inlet area ofsaid inlets, and a pair of flame stabilizers disposed in said tube, oneat each end thereof.

6. An internal combustion burner as claimed in claim 5, wherein each ofsaid exhaust orifices has a width equal to at least a major fraction ofthe wall thickness defining said orifices.

7. An internal combustion burner as claimed in claim 5, wherein thecross-sectional area of said tube is about 6 times the totalcross-sectional area of said inlets.

8. An internal combustion burner comprising a tube of maximum wallthickness less than the maximum internal cross-dimension of said tube,cap means plugging both ends of said tube, a row of spaced exhaustorifices extending along one side of said tube, each of said exhaustorifices having a width equal to at least a major fraction of themaximum thickness of said wall, each said cap means having an inletpassage extending therethrough and communicating with the interior ofsaid tube for injecting an air-fluid fuel combustible materialcontinuously into said tube from opposite ends thereof for combustionwithin said tube with discharge of the products of combustion throughsaid exhaust orifices and the ratio of the total cross-sectional exitarea of said exhaust orifices to the total cross-sectional inlet area ofsaid inlets being from about 2:1 to 8:1, and a pair of flame stabilizersdisposed in said tube, one at each end thereof.

9. An internal combustion burner comprising a tubular housing forming acombustion chamber, a row of uniformly spaced orificesextending'longitudinally along one side of said housing, and coolingmeans for portions of said housing comprising a pair of cooling channelsextending longitudinally of said housing on each side of and in parallelrelation to said row of orifices, a compensating cooling channelextending along said housing in diametrically opposed relation to saidrow of orifices, and means for connecting said cooling channels to asource of cooling fluid.

References Cited by the Examiner UNITED STATES PATENTS 971,105 9/1910Bausher 126271.3 1,138,549 5/ 1915 Frederickson 158-27.4 1,514,81511/1924 Anderson 15 8--27.4 1,660,018 2/ 1928 Steffen 1581 14 X2,385,107 9/ 1945 Scherl 15827.4 2,781,754 2/1957 Aitchison et al l2,826,248 3/1958 Angel 158-99 2,878,644 3/1959 Fenn l584 3,118,489 1/1964 Anthes 1587 FREDERICK L. MATTESON, JR., Primary Examiner.

MEYER PERLIN, Examiner.

V. M. PERUZZI, E. G. FAVORS, Assistant Examiners.

1. AN INTERNAL COMBUSTION BURNER COMPRISING A HOLLOW CYLINDER OF MAXIMUMWALL THICKNESS LESS THAN THE MAXIMUM INTERNAL CROSS-DIMENSIONAL OF SAIDCYLINDER, CAP MEANS PLUGGING BOTH ENDS OF SAID CYLINDER, A ROW OF SPACEDEXHAUST ORIFICES EXTENDING ALONG ONE SIDE OF SAID CYLINDER, A PLURALITYOF INLETS LEADING INTO SAID CYLINDER FOR INJECTING AN AIR-FLUID FUELCOMBUSTIBLE MATERIAL CONTINUOUSLY INTO SAID CYLINDER FOR COMBUSTIONWITHIN SAID CYLINDER WITH DISCHARGE OF THE PRODUCTS OF COMBUSTIONTHROUGH SAID EXHAUST ORIFICES, AND THE TOTAL CROSS-SECTIONAL EXIT AREAOF